A simultaneous Emission/Transmission Computed Tomography (ETCT system possesses the advantage of both SPECT and CT by offsetting the individual weakness of each. However, the successful development of ETCT machine must include improved spatial resolution which currently is limited by the X-ray and gamma ray detectors systems used. Scintillation cameras used in SPECT are essentially at their limit of spatial resolution. Silicon photodiode detectors used in CT are limited by sensitivity. The most promising detectors for this application are solid state detectors like HPGe and CdTe. THE cryogenic requirement of HPGe makes CdTe a unique candidate for the ETCT innovation. Our recent progress during the Phase I project with CdTe X-Ray and gamma-ray detectors and arrays is very encouraging. Further research into this promising system has high potential of producing a new detector technology with better performance, which could be the basis for a future generation of medical imaging instruments like ETCT. The goal of this Phase II program is to construct and test a fully prototype CZT array in ETCT instruments. PROPOSED COMMERCIAL APPLICATIONS: This work would lead to the development of CDT detectors for simultaneous emission/transmission CT. This new generation of instrument will have an enormous impact on nuclear medicine with more complete data for diagnosis and treatment of patients. The market it would create will be equivalent to that of CT and SPECT today. There is also a major nonmedical market for improved X-ray sensors.